A problem with existing manually operated piston pumps is that the arms or leg(s) of the user of the pump are loaded directly. The force that needs to be applied to operate the pump increases with every stroke, if the pressure of a gaseous and/or liquid medium inside a closed body, e.g. a tyre, is to be increased. The force remains the same if the medium is a non-compressable liquid, as e.g. water in water pumps. This gives the user a wrong feeling. In the design process the magnitude of these forces is often decided as a compromise between the expected weight and the initiating power of the arms or leg(s) of the user and the time it takes to pump the body. The diameter of the piston defines the level of force to be applied to operate the pump. The pumping time is also defined by the length of the cylinder of the pump. This limits the use of the pump to persons of a certain height. Bicycle and car pumps are clear examples. Especially high-pressure pumps are optimized for male users (design starting point: 75 kg weight, 1.75 m length) despite the fact that women and teenagers make up the largest group of racer bike users.
When pressures ranging from 4–13 Bar have to be optained using the same pump, e.g. a high-pressure bike pump, the combination of low pumping time for low-pressure high-volume tyres and low forces for high-pressure low-volume tyres becomes a problem, if the pump is a hand-operated (floor)pump. If a low-pressure tyre with a relatively large volume has to be pumped by a high-pressure pump, it takes longer time than necessary and the user does not feel any reaction forces at all which gives the user a wrong feeling. It is often difficult to get the right tire pressure of a high pressure tire with e.g. a high pressure floor pump, because often only a part of a last pump stroke is required, mostly not at the end of the stroke. Therefore it is difficult to control the movement and stop of the piston because of a too high operating force. New types of bicycles and tyres were introduced at the beginning of the 1980's. These new bicycles are widely used as transportation means. Therefore, universal piston pumps have been observed in the patent literature. These pumps can pump both low-pressure and high-pressure tyres by means of a reasonable amount of force and time. This is accomplished through the simultaneously application of several coaxial/parallel cylinders and pistons that can be switched on and off (e.g. DE 195 18 242 A1, DE 44 39 830 A1, DE 44 34 508 A1, PCT/SE96/00158). These solutions are expensive and sensitive towards malfunctioning due to the fact that key parts are incorporated in the pumps several times.
A bicycle floor pump which has from the outside the form of a pure single truncated cone with a movable piston is known from the early bicycle literature. The aim is apparently to reduce the operating force, as the cone is standing upside down. There exists apparently no prior art of pistons which can move in a chamber with different diameters and which seal properly and tight. This is not surprising because it is not so easy to produce a reliable piston of that kind, specifically not with the state of the art at that time even when only low pressure high volume tires existed. A leakage would not cause a big problem for such a consumer product. For current high pressure pumps or those for professional purposes it is descisive that no leakage exist. The demands towards the piston construction for high pressure levels and/or low and high pressure levels, causing no leakage are different from those which solely have to do with lower pressure levels.
U.S. Pat. No. 5,503,188 concerns an organical constructed pipeline flow stopper with an inflatable impervious bag. This stopper cannot be compared with a moving piston. In a pump can the media to be compressed and/or moved continuously cause a dynamic load on the piston while the wall of the pressurized chamber of the pump can change its cross-section regarding area and/or shape perpendicular to the direction of movement of the piston between one point and another which gives specific sealing problems. These sealing problems are solved by the present invention.
GB 2 023 715A and GB 2 070 731A concern pumps with a cylinder having a slight internal taper due to production technical reasons as the cylinders are being diecast moulded. The taper aims the cylinder be able to be taken out of the mould. The piston has a seal having a feather end respectively two split seal rings displacebly supported by the piston to remain fully effective throughout the whole stroke. A taper of 0.15 mm on a diameter of 50–100 mm cannot be compared with those of the present invention, as the reduction of the area between two transversal cross sections along the longitudibal axis of the chamber is so small (approx. 0.5%) that it has almost no effect on the circumferical length of the transversal cross-sections, or on the operating force of the pump during the stroke, also because the pressure in the pump is very low. The small feather edge respectively split seal rings of the piston can easily tighten the very small above mentioned taper. The pistons shown in the present application cannot be compared with those of this prior art, as the present pistons are primarily designed to overcome changes in the transversal cross-sectional area's of a much bigger magnitude. The tapers illustrated in the present invention are on scale (unless otherwise stated) and not for ease of illustration exaggerated as it is the case in GB 2 070 731A.